This invention relates to envelope control systems for electronic musical instruments in which digital data representing musical sound waveforms is read out from a memory for producing musical sounds with the envelope thereof controlled.
Recently, in the field of electronic musical instruments, the main circuit of the instrument is constructed by using digital techniques. In this technology, digital data representing musical sound waveforms are stored in a waveform memory and are read out under the control of read-out clocks corresponding to note frequencies or with a read-out clock of a fixed frequency for all the notes but with different phase angles according to the note frequencies, thereby producing musical sounds having predetermined waveforms.
In the waveform memory, sampled data of a waveform of a predetermined natural musical instrument for one period is stored. Alternately, data of a waveform of a predetermined function, for instance a sinusoidal waveform data, is stored. When reproducing musical sound by reading out the waveform data stored in the waveform memory, envelope control of the musical sound is also done. To this end, it is necessary to multiply the digital waveform data and digital data representing the envelope by using a multipler.
To correctly calculate the amplitude value of the envelope controlled musical sound waveform by using the multipler, it is necessary to make calculations on all the bits constituting the waveform data and envelope data and derive the result of multiplication, for instance down to data of lower significant bits than the same number of bits as the bit number of both the waveform and envelope data. Therefore, the multiplier of whatever calculation system used to this end, renders the overall circuit construction more complex with increasing bit number and constitutes an obstacle when it is intended to integrate the circuit of an electronic musical instrument.